Heat treating furnace



Feb. 28, i939. H. J. STEIN 2,149,245

HEAT TREATING FURNAGE Filed Deo. 9, 1936 2 VSheets-Sheet l Feb. 28, 1939. H. J. STEIN 2,149,245

HEAT TREAT ING FURNACE Filed Dec. 9, 1956 2 Sheets-Sheet 2 Patented Feb. 28, 1939 UNITED STATES PATENT- OFFICE HEAT TREATING FURNACE Application December 9, 1936, Serial No. 114,980

20 Claims.

Another object is to provide a furnace having a central ring tube, a parabolic reflecting surface overlying said tube, an annular heating zone and a source of radiant energy in said tube substantially at the focal point of said surface whereby the radiant' energy will be uniformly reflected throughout the heating zone.

Another object is to construct a furnace in Which central firing, a concave or parabolic reflecting or deecting surface and one or more heating zones are so correlated that the conditions of temperature, pressure and atmosphere are uniform throughout each heating zone.

Another object is to construct and operate a rotary heat treating furnace, in which central firing, a concave or parabolic reflecting and deflecting surface and one or more heating zones are so correlated that each piece of stock is always subjected to the same conditions of temperature; pressure and atmosphere for exactly the same. period of time to thereby produce work of uniform quality.

Another object is to provide means for carrying out the aforementioned mode of operation and control.

Another object is to provide a control system including a temperature indicating device which is rendered operative as a control means only when it is capable of rendering accurate temperature indications.

Another object is to provide a centrally fired furnace which is compact, cheap to manufacture, and easily repaired and which rotates as a unit, thereby eliminating relative rotation between parts and the necessity for providing the usual ineffective and troublesome seals.

The invention, accordingly, consists of the mode of operation and features of construction, combinations of elements and arrangement of parts as more particularly pointed out in the appended claims and in the detailed description, reference being had to the accompanying drawings, in which:

Fig. 1 is a central, vertical section through a rotary furnace embodying the invention;

Fig. 2 is a sectional plan view of the furnace taken on the line II-II of Fig. 1 showing the arrangement of the upper charging openings, 5 the gas discharge ues, the pyrometer tubes and the slotted partition means;

Fig. 3 is a sectional view'of a furnace taken along the line III-III of Fig. 1, showing the arrangement of the lower firing openings, the ring tube and the channels for discharging slag;

Fig. 4 is a fragmentary side elevation of the annular shield showing the relative arrangement ofthe charging openings which are arranged to coincide with those in the furnace;

Fig. 5 is a vertical sectional view showing a modified arrangement in which the protecting shield moves bodily with the furnace; and

Fig. 6 is a schematic showing of the furnace embodying the control system.

Referring to Figs. 1-3, it is seen that the furnace, per se, comprises a top or a roofed portion I and a lower or body portion 2. The body portion includes a circular metal base plate 3 l having a, central opening 4 and an upstanding 25 annular flange 6 `adjacent its outer periphery. An annular metal' side wall casing 1 has its in- Vner surface adjacent its lower edge surrounding fand in telescopic relation to the upstanding ange 6 with its lower edge resting on the base 30 plate 3 to be supported thereby; the upper portion of the casing l having formed or mounted thereon, in any desired manner, an annular upwardly opening sealing channel 3. Boxlilte slag pockets 9 extend outwardly from the lower 35 edge of the casing 1; the pockets being equally spaced circumferentially thereof and attached to or formed integral with the slag spouts in any'desired manner. Obviously the slag pockets may be secured to the furnace casing 1 instead 40 of to the slag spouts 25 if it is so desired.

An annular metal collar ll cooperates with the central opening in the base plate 3 to define a burner opening i 2 and a centrally positioned, upwardly flaring firing tube I3, formed of any suitable heat resisting material, extends upwardly into the furnace a material distance in coaxial relationship with said opening. 'Ihe inner surface off the metal side Wall 1 and the base plate 3 are covered with a layer of any suitable insulat- 50 ing material It which is in turn covered by a relatively thick layer of ceramic or other high heat resistant material I5; A plurality of horizontally extending and circumferentially spaced members f6 bridge the space between the upper 55 f|9 through lwhich thefiue lgases pass from the f upper zone downwardly into the lower zone.

portion ofthe firing@ tube and theLinner-surface of the side wall and divide the space between the firing tubeandside wall into an upper high heat zone IT and a lower, 10W heat zone` I 8,'with the spaces betweenfsaid members providing passages plurality of'r circumferentially spaced vertically yextending hues .20 are formed onA the inner sur-r face of the side wall kwith their lower iends'in. f communication ywith the low heat zone at a pointy adjacent they base. and side wall for conducting `the iiue gases fromthelowheat zone lto the i atmosphere.A The furnace side wall is provided with four vertically spaced series of` openings,l 2|, 22, 23 and24, the openingsin each series being f lequally .spacedcircumferentially of the furnace. fThe lowerfopenings ZI-are in vertical'alinement f with the slag pockets 9 and are inclined upwardlyl and inwardly withtheir inner ends forming conconstitute; charging-y openings for the lowy heat zone; the stoekwhich is 'inserted' .through ysuch openihgslying directly beneath a member' |6 to ybe `,shielded thereby from any slagA or Alikelm terial which might be discharged from the high l heatzone. downwardly ythrough the passages I9 into. the low heat-zone. `The 'next' higher series 'l #of .openings 23kfoyerlie every fourth memberr |63' andy consti-'utc charging openings for thek high .heatzona l The upper series of openings 24 are,l positionedadjacent the chargingopeningsforthe high heat Zone and, extending through each open--y ing 24 and into the furnace, is a radiating type pyrometer tube 26 which may be constructed of any suitable material such as silicon carbide.

Depending from the base plate 3 are at least.

three equally spaced bifurcated brackets 28 each carrying a shaft 29 on which is mounted a roller 3| with either the roller being slidably and rotatably mounted on the shaft orl the shaft being slidably and rotatably mounted in suitable bearings formed in the bracket with the roller fixed thereon so that the furnace and brackets may move laterally relative to the rollers. vI'he inner leg of each bracket 28 extends downwardly to a point beneath the roller and terminates in a horizontally and inwardly extending flange 32 for supporting the ring gear 33 which is secured thereto in anysuitable manner as by capscrews 34. The base structure 36 includes an annular member 31 having its upper surface providing a track 38 for the rollers 3|; the track comprising an outer and upwardly extending vertical retaining portion 39 and an inner upwardly inclined roller supporting surface 4|. The rollers 3| have their supporting surface beveled to engage the inclined surface 4| of the track 38 and are retained against outward movement by the retaining portion 39 and against inward movement by the aforesaid inclined surface. The furnace is rotated by means of an electric driving motor 42 which, through a reduction gearing mechanism 43, slowly rotates a' shaft 44 which is supported in bearings 46 carried by the annular base member 31. The inner end of the shaft 44 carries a pinion 41 which ciated with the :motori 4.2 is a magnetic breaking' f mechanism 48 of known construction.

n lThe roof or top portion has an inner' parabolicl f surface 49 overlying the centrally positioned firing ltube |3 and the annular highy heat zone Il with its focal point lying on the axis ofthesaidt'ube'so that f when the burner is operated to terminate its flame,

' which constitutes a source of radiant energy, sub# o stantially at? such point,l theemitted rays will ber reflected from said surface downwardly and uni# formly throughoutfthe high heat zone. In addition, if the burner is operated sol that the ame impinges on the concave surface 49, the gases ywill lbe ldeflected yand uniformly distributed throughout the heating zone. In this'ce'on'nec'tionA it should be obvious that` although'the upwardlyr f flaring firing tube I3 shields the name from cross y l rdrafts and other conditions tendingl to'p'ro'du'ce f unequalconditions.y of temperatura; pressure and atmosphere, it also permits the iiame to diverge l prior to impinging on the concave 'surface 49 and f 1 f as a result the velocity of the flame is materially f reduced andafter.impingingon said surface, ap`` l i ,25 towards the side wall.; However 'the luniform f pears to; slowly roll or billow radially 'outward ydowndraft effect produced rbythe plurality of' equally and circumferentially spaced fiues Acauses jl f 1' the flamefto descendruniformly throughout'the f f yheatingizone. f yThe ,topr portion comprises a rela l tively thick inner layer yof ceramic 'orv other highl I `heat resistant: material 5 an 'outer' layer 'of' in-r n taining member 53 having an.y upwardly land is" L wardly`r extending retaining yflanger 55' and van outwardly extending horizontal portion that teri-f Esealing flange 54 which, when 'the topportion is in itsproper position,-extends into the annularsealing channel 8 formedA on the' sidewall Al.r jIty f should be understood that'ther channel 8 ris subl'sulating material y52 and any annular metal ref minates .in a downwardly dcpe'ndir'ig'l annular f vide a flat annular seating surface 51 which cooperates with a like surface presented by the top of the side wall proper. Three equally and circumferentially spaced vertically extending flue passages 58 are provided to form continuations of the vertical flue passages 20 in the body portion 2. The top or roof portion is also provided with eye bolts 59 which are for the purpose of bodily lifting the roof from the body portion 2. In a like manner the body portion may also be providedwith a similar arrangement (not shown) or the spouts 25 may be considered an equivalent arrangement whereby the body portion together with the top, if desired, may be lifted bodily rial and also the insulating material, may either be assembled in block form or suitable molds may be employed and the refractory and insulating material inserted while in a plastic state. The firing tube I3 and the partition members I 6 may also be constructed in any preferred manner and, if desired, in accordance with the examples set forth above in connection with the wall and roof structure. I

An annular shield El surrounds the side wall of the furnace in spaced relation thereto and is supported upon stationary leg structures 62. The shield is provided with four openings 63 (see Figs.

*2 and 4); the upper opening receiving a pyrometer device comprising a thermocouple 94; the next lower opening being in vertical alinement with the upper series of changing openings 23; and the two lower openings being in vertical alinement with the lower series of charging openings 22 so that when the furnace is rotated relative to the shield the pyrometer tubes 2B will successively come into alinement with the thermocouple 9d and in a similar manner the upper and lower charging openings will likewise successively come into alinement with the corresponding openings in the shield, attention 'being directed to Fig. 4 which clearly shows that at the time the upper charging opening is in alinement with the corresponding opening in the shield, two lower charging openings, one on each side of the upper charging opening, are simultaneously alined with the two lower openings in the shield 6I. An annular blast pipe 66 is positioned near the lower edge of the shields 6l and is supported thereby in any suitable manner (not shown) and has an annular series of upwardly directed openings 66 (see Fig. 3) for directing an annular sheet .of air upwardly adjacent the inner surface of the shield so as to protect the operator from the heat issuing from the furnace through the charging openings. The lower edge of the shield is spaced above the slag pockets 9 and the lower edge of the spouts 25 so that an instrument may be inserted into the outer portion of the slag openings 2| for clearing or cleaning the same.

Fig. 5 shows a modified form of structure in which the shield is supported by the furnace for movement bodily therewith, it being understood that, in this arrangement, the'total number of openings and their arrangement must conform with the total number and the arrangement of the charging openings in the furnace side wall. In this .case the blast pipe et must be supported independently of the shield 6l by any suitable means such as stationary brackets 10 (only one of which i's shown). The supporting means for the shield in this modification comprises a bolt 68 extending through the shield and the outer upstanding edge of the sealing channel 8 with a suitable. spacing member 69 therebetween. Only one of. the supporting means for the shield 6l is shown in Fig. 5, but it should be understood that a suflicient number of bolts and spacing members are employed at spaced intervals'to securely mount the shield on the furnace in the manner indicated. l

Operatively associated with the burner opening l2, which is coaxial with the firing tube i3, is a burner 1I supported on a bracket 12 which is in turn supported by a beam member 13 carried by the annular base ember 31. The burner, when operating, will direct a flame axially of the ring tube i3 which defines an upward flaring flame conning passage which is generally circular in cross section as shown in Fig. 1 and the length of the name can be adjusted so that its hottest portion is substantially at the focal point of the parabolic inner surface 49 for the purpose hereinbefore set forth.

'I'he use of a concave or a parabolic reflecting surface overlying the central firing tube and annular heating zone insures a uniform distribution of the heated gases throughout said zone and, when a source of radiant energy, for example the burner flame as previously described, is positioned substantially at the focal point of said surface, the emitted rays will be reflected downwardly and uniformly throughout the heating zone. The annular baille structure comprising the members I6 together with the equally and circumferentially spaced flues .20 operates to maintain a relatively high pressure throughout the heating zone or zones at all times thereby preventing cross drafts and an unequal distribution of heat. The construction of the furnace as a unit for bodily rotation about a vertical axis results in a compact unitary structure which entirely eliminates relative rotation between parts and the necessity for providing seals.

The illustrated furnace, which is especially designed for use in welding plow shares on a production basis, is charged and operated in the following manner: assuming that the burner has been placed in operation in the usual and well known manner and that the furnace temperature has reached its normal value, a plow share 14 is inserted through the lower right hand opening in the shield 6l and into the furnace through the charging opening in the lower series 22 which is alined therewith and rotation of the furnace is started by closing the circuit of the driving motor d2. As alternate charging openings in the series 22 come into alinement with the aforementioned opening in the shield, which occurs at each 120 of rotation or 1/3 revolution, rotation of the furnace is stopped for a short interval (preferably automatically as hereinafter disclosed) and a plow share is inserted as hereinbefore set forth. At the end of one complete revolution the lower heat zone will then contain three plow shares inserted through charging openings spaced 120 apart. During the next complete revolution of the furnace three additional plow shares will be inserted in a like manner in the openings which become alined' with the lower left hand opening in the shield (see Fig. 4) which is spaced 60 from the previously mentioned right hand opening. At the end of two complete revolutions the lower heat zone will be completely charged (containing six plow shares) and the plow share initially inserted will be in alinement with the lower right hand opening. During the interval the furnace is at rest the last mentioned plow share will be withdrawn from the low heat zone .and inserted into the high heat zone through the upper opening in the shield (see Fig. 4) which during the interval the furnace is at restis always in alinement with lone of the charging openings in the high heat zone. This process is continued until the high heat zone is completely charged i. e., contains three plow shares and thereafter during the interval when the furnace is'at rest a plow share is withdrawn from the high heat zone, the appropriate plow share in the low heat zone is removed -and inserted into the high heat zone and a new plow share is inserted into the low heat zone. Thus it is seen that each plow share remains in the furnace during three complete revolutions, two in the low heat zone and one in the high heat zone, thereby subjecting each plow which passes through the furnace.

share tothe same conditions of pressure, temperature and atmosphere for the same period of time. This procedure results in an equal and uniform treatment of each and every plow shar ,The invention is obviously not limited solely for the heat treatment of plow shares as it can readily be employed for heat treating other articles and in this connection, it may be well to point out that the number and spacing'of the charging openings, the speed and rotation of the furnace and the stopping intervals may be varied as desired in order to satisfy the requirements of the particular heat treating process used. In addition, it should be understood that a particular number of heat treating zones is not essential in order to carry out the spirit of the invention and that it can be readily applied to furnaces having any desired number of such zones but not less than one. The members I6 which divide the interior of the furnace into low and high heat zones as previously described may be varied in number and shape as desired or the partitioning means may be formed as an integral structure having openings or passages extending therethrough for the purposes described.

Fig. 6 is a schematic illustration of the previously described furnace embodying a preferred control arrangement for eifecting a desired mode of operation in connection with the welding of small stock, such as plow shares, on a production basis. The various control elements employed in the above referred to arrangement to effect the desired operation are old per se and are shown as cooperating diagrammatically in order that the general mode and sequence of operation can be readily and thoroughly understood.

The furnace is mounted for rotation about a vertical axis on the base structure 36 and is rotated in a clockwise direction by means of the ring gear 33 which meshes with the pinion 41 fixed on the shaft 44. 'I'he motor 42 is connected to the shaft 44 by means of the reduction gearing mechanism 43 and operatively associated with the motor 42 is a magnetically operated braking mechanism 48. The motor 42 and the braking mechanism 48 being connected Ato a common source of power, line 16, by means of the conductors 11. A solenoid operated switch 18, which is biased toward open position by means of aV spring 19, and a normally closed, manually operated switch 8| control energization of the motor 42 and braking mechanism 48; the latter being operative`when deenergized to almost immediately stop rotation of the motor and furnace.

The burner unit illustrated includes a motor driven blower 82 for supplying air under pressure through the pipe 83 and a fuel supply pipe 84. Suitable valves 86 and 81 respectively control the flow of fuel and air through the pipes 84 and 83- and to the burner and, as shown, are mounted on a common stem 88 for simultaneous actuation by means of a suitable reversing motor 89 which isA operatively connected tosaid stem by a crank and link mechanism 9|.

A temperature indicator 92, of the Leeds and Northrup type, has a solenoid actuated indicating arm or pointer 93 which,`as viewed in Fig. 6, moves from the position shown in a clockwise direction upon a decrease in temperature and in a counterclockwise direction upon an increase in temperature.

The furnace is provided with pyrometer tubes 26 of any suitable material which extend through the side wall of and into thefumace at a point adjacent to each of the charging openings in the upper or high heat zone. A sensitive thermocouple 94 (of known construction) is iixedly mounted on a stationary structure, preferably the annular shield 6|, so as to be opposite one v |02, one near each charging opening in the high heat zone which operate, when the furnace is rotated to successively contact a normally open switch |03 to momentarily close the same and thereby energize a circuit comprising one side of the line |04, wire |06, switch |03, wire |01, solenoid |08 of switch |09 and wire back to the other side of the line. Switch |09 is of the opposed solenoid, snap acting type and comprises solenoids |08 and ||2, switch blade 3, a biasing spring ||4 and the contacts I6 and ||1. Energization of the solenoid 2 moves the switch blade ||3 to engage the contact ||1 thereby closing a circuit including one side of the line 04, wires 8 and ||9, the motor switch solenoid |2|, wire |22, contact 1, switch blade ||3, and wire |23, back to the other side of the line. Energization of the solenoid |08 moves the switch blade 3 to engage the contact ||6 thereby closing a Circuit comprising one side of the line |04, wire |23, wire |24, solenoid |26 of a duration timer or retarded relay |21 and wire |28 back to the other side of the line |04. The duration timer or retarded relay comprises a solenoid actuated switch |29 having a dashpot arrangement |,3| which prevents the switch |29 from bridgingthe contacts |32 for a predetermined time interval (fteen seconds in this particular arrangement) after energization of its actuating solenoid |26.

A Stromberg'electric clock |33 has its driving motor |34 continuously energized through conductors |35 connected to the line |04 through a manually operated switch |31. .The dial |38 of the clock is calibrated in any desired increments of time, preferably seconds, and the setting hand |39 may be moved by means of a knob |4| to any predetermined position depending upon the particular timing interval desired. Pressing the starting button |42 connects the hand |43, which is biased to the position shown, .with a driving mechanism actuated by the motor |34 whereupon it commences to move slowly in a clockwise direction and continues such movehand |39 at which time the connection with the v driving mechanism is released and the hand immediately returns to its initial position and, due to its inertia, strikes the resilient blade |44 Causing Ait to momentarily engage a similar blade |46. The hand |43 would then continue to move and repeat the previously described cycle of operation unless some means were provided for stopping its operation which, in the present instance, comprises a button |41, operable when pressed, to disengage the hand |43 from its driving mechanism whereupon it immediately returns to its initial position and no further movement will take place unless the starting button is again pressed. Y

at the point indicated by the arrow |69 with the The so-called stopping of the clock with the hand |43 in its initial position is automatically accomplished by means of a solenoid |48 which, when energized, presses the'button |41 to stop the clock in the manner previously described; the aforementioned resilient blades` |44 and |46 constituting a switch which momentarily closes a circuit including the solenoid |48. Thus it is seen when the hand |43 reaches the setting hand |39 it immediately returns to its initial position, and closes the switch comprising the resilient blades |44 and |46 thereby energizing the solenoids ||2 and |48. The starting button |42 is operatively associated with Ithe solenoid |49 which, when energized, presses the starting button to start the clock as previously described. 'I'he solenoid |49 is in circuit with the duration timer switch |29, the reversing motor 89 and the solenoid switch |5| as follows:

One side of line |94, wire |52, solenoid |49, wire |53, switch |5|, wire |54, switch |29, wire |56, the reversing motor 89 and wire |51 back to the other side of the line |94.

The contact 98 of the temperature indicator 92 is resilient and, if the temperature becomes excessively low, pointer 93 will move this contact to the left until the pointer engages stop |9| which closes a circuit. from oneside of the line |94 through wires |51 and |58,-pointer 93, contact |9|, wire |59, solenoid |6|, wire |63, solenoid |62 and wire ||6 back to the other side of line |94. Solenoid |6| closes its switch and a circuit through wires |64 and |66 which energizes solenoid |48 to stop the timing clock |33. Solenoid |62 actuates switch |5| to open the circuit including the starting solenoid |49 and closes a shunt circuit about the latter which prevents its reenergization and rotation of the furnace until'the temperature again reaches the normal value. The spaced contacts 98 and 99 of the temperature indicator 92, which are adjustable, are preferably spaced so as not to permit a temperature deviation of more than a few degrees in either direction. A greater deviation will cause the pointer 93 to engage one or the other of the contacts 98 and 99 to energize the reversing motor 89 and effect a corresponding regulation of the fuel and air, to maintain the temperature within the desired limits.

The normal operation of the furnace will now be described it being assumed that the furnace is completely charged with stock as Shown in Figs. 2 and 3, i. e. with six pieces in the low heat zone and three in the high heat zone and that the point of charge is indicated by the arrow |69 in Fig. 6. With the various control elements in the positions shown in Fig. 6, the driving motor 42 and the 4electromagnetic brake 48 are energized and the furnace is rotating in a clockwise direction as indicated by the arrow |1I.

When the projection |92 engages and closes the switch |93, a circuit will be energized cornprising one side of the line |94, wire solenoid |98 of switch |99, wire |91, switch |93 and wire |96 back to the other side of the line |94. Energization of solenoid |98 will move the switch blade ||3 from engagement with contact ||1 and into engagement with thecontact ||6. Breaking the connection withl contact ||1 will open the circuit comprising one side of line |94,

Wires ||8 and ||9, solenoid |2| and wires |22` and |23 back to the other side of the line, thereby immediately deenergizing the driving motor and the braking mechanism whereupon the furnace will stop with the charging opening thermocouple 94 in alinement with one of the pyrometer tubes 26. Connecting the blade ||3 and contact 6 will close a circuit comprising one side of the line |94, wire |28, solenoid |26 of the duration timer |21, and wires |24 and |23 back to the other side of the line |94. After approximately fifteen seconds, the switch |29 will bridge the contacts |32 completing a circuit including one side of the line |94, wire |51, the armature winding of the reversing motor 89, wire |56, Wire |54, switch |5|, the clock starting solenoid |49, the wire |52 back to the other side of line |94. The delay of fteen seconds provided by the duration timer is necessary in order to obtain an accurate temperature indication and prevent improper regulation of the burner as it is obvious that during the time interval required for the furnace to rotate 120, the space between the projections |92, the thermocouple 94 will have cooled down considerably and upon realinement with a pyrometer tube would not instantaneously render a correct indication of the .furnace temperature, and, as a result, the pointer 93 would engage contact l98 Ithereby energizing the motor eld winding 95 and since the armature winding 99 is also energized, the motor 89 will rotate so that the fuel and air valves would be opened more each time the previously described cycle of operation ,was repeated. ,If i the temperature of the furnace becomes either too low or too high while the switch |29 engages contacts |32, the indicator pointer 93 will engage with one or the other of contacts 98 and 99 and energize one or the other'of the field windings 95 and |99 to thereby rotate the control motor 89 in a direction to eectthe necesary burner' regulation, However, if the temperature is sufficiently low to cause the pointer 93 to also engage contact |9| such engagement will close a shunt circuit about the armature and eld windings 99 and 95, respectively, of the motor 89 which is effective to maintain the motor inoperable. This shunt circuit comprises one side of line |94, wires |51, |58, pointer 93, contact |9|, wire |59, solenoid |6|, wire |63, solenoid |62 and wire ||8 back to the other side of line 194.

Energization of the starting solenoid |49 will start the clock hand |43 moving towards the setting hand |39 and. when it returns to its initial position as previously described, it will close the resilient contacts |44 and |46, thereby energizing a circuit comprising one side of the line |94, wire wire |64, stopping solenoid |48, wire |66, solenoid ||2 of switch |99, wire |61 and wire |68 back to the other side of the line |94. Energization of solenoid |48 stops the clock with the hand |43 in its initial position while energization of solenoid ||2 engages the switch blade ||3 with contact ||1, thereby energizing the driving motor 42 and the braking mechanism 48 and deenergizing the duration timer |21. Energization of the driving motor starts the furnace rotating through another cycle of operation as previously described and deenergization of the duration timer |21 opens the circuit of the burner control motor 89 and the starting solenoid |49 of the time clock |33.

The time interval consisting of the aforementioned fifteen seconds and the time required for.

the clock hand |43 to move from its initial position to the setting hand |39 and back to its initial position, provides the time necessary to remove a piece of stock from the high heat zone,

- falls below the lower limit, continued operationy transfer another piece from the low heat zone into the high heat zone and to place a new piece in the low heat zone. In other words, with the particular number of charging openings employed, a piece of stockremains in the furnace during three complete revolutions. However, it should be understood that the number of pieces of stock in the furnace at any one time may be varied as may also the stopping interval and the rate of and the number of revolutions made by the furnace to complete any desired or preferred cycle of operation. Moreover, the previously described mode of operation is obviously applicable to furnaces having any desired number of charging openings and only a single heat zone. The furnace is prevented from rotating during intervals when the temperature is excessively low by means of the circuit closed by thepointer 93 and the contact or stop |04 of the temperature indicator as previously described and, it may be well to again point out, that when the aforementioned circuit is closed, the burner regulating motor is inoperative since the motor windingsare shunted by the wire 158 and the rate of ring remains the same until after the furnace reaches the normal operating temperature which will occur due to the fact that no new or cold material is being inserted for heat treatment and therefore the heating requirements have been materially reduced. In other words, the firing rate necessary to maintain the heating zone or zones at any desired temperature will depend, excepting the usual heat losses,

r.upon the rate of heat utilization and since the iin'ng rate is only varied between narrow limits, it necessarily follows that if the temperature of the burner withdut utilizing the generated heatwill quickly raise the temperature to within the desired limits. However, it should be understood that if the lowering of the temperature is due to faulty burner operation which continues and might be caused by failure of either the fuel supply or the blower motor, then it will be necessary to remedy such defect before the furnace will continue to operate in the normal manner as hereinbefore described.

. It should be understood that Athe power lines i 'I6 and |04, although shown as being entirely independent, can obviously be interconnected either directly or by means of a stepdown transformer if the Acontrol system proper is to be operatedl at a relatively low potential'. Moreover, while the automatic switches or relays are shown as being closed when their actuating solenoid is energized, it is obvious that if it, is desired, the opposite mode of operation may be employed and that any other suitable means may be used to effect actuation of the switches' or relays in the manner described.

In view of the foregoing, it is readily seen that the controlling factors in any heat treating operation, time and temperature are accurately controlled at all times to thereby produce work of uniform quality.

The previously described mode of operation insures an identical treatment of all stock thereby producing products of uniform quality and eliminates practically all of the waste that normally results from poor judgment or guesswork on the part of the operator or attendant.

Although but a few embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes ,and modifications may be made vtherein without departing from the spirit of the invention or from the scope of the appended claims.

It is claimed and desired to secure by Letters Patent:

1. A generally circular heat treating furnace comprising a base having a centrally disposed, upwardly extending firing tube, a side wall surrounding said tube, a roof overlying said base and tube, means extending from said ring tube to the side wall and dividing the interior of the furnace into upper and lower communicating heating Zones, and a plurality of circumferentially spaced discharge fiues communicating with said lower heating zone at a point near said base and the inner periphery of the side wall.

2. A generally circular heat treating furnace comprising a base having a centrally disposed, upwardly extending firing tube, a side wall surrounding said tube, a roof overlying said base and tube, means extending from said firing tube to the side wall and dividing the interior of the furnace into upper and lower communicating heating zones, said side wall having vertically spaced series of openings providing access to the upper and lower heating zones for inserting and withdrawing stock, and a plurality of circumferentially spaced, discharge ilues communicating with the lower portion of said lower heating zone.

3. A generally circular heat treating furnace comprising a base having a centrally disposed, upwardly extending firing tube, a side wall surrounding said tube, a roof overlying said base and tube, means extending from said firing tube to the side wall and dividing the interior of the furnace into upper and lower communicating heating zones, said sidewall having vertically spaced series of openings providing access to the upper and lower heating zones for inserting and withdrawing stock, a plurality of circumferentially spaced discharge nues communicating with the lower portion of said lower heating zone and an annular shield surrounding said side wall and having vertically spaced openings alined with the vertically spaced series of openings in the side wall.

4. A generally circular heat treating furnace comprising a base having a centrally disposed, upwardly extending ring tube, a side wall surrounding said tube, a roof overlying said base and tube, means extending from said firing tube to the side wall and dividing the interior of the furnace into upper and lower communicating heating zones, said side wall having vertically spaced series of openings, a pyrometer tube extending into the furnace through each opening in the upper series with the next two lower series constituting charging openings providing access to the upper and lower heating zones, a plurality of circumferentially spaced discharge flues communicating with the lower portion of said lower heating zone, means supporting said furnace for bodily rotation about a vertical axis, a stationary shield surrounding said side wall and having vertically spaced openings alined with the series of charging openings and a pyrometer alined with said pyrometer tubes so that, when the furnace is rotated, a pyrometer tube and a charging opening in each series will simultaneously come into alinement with the pyrometer and the openings in said shield. f

5. In a combination comprising a generally circular, centrally nred heat treating furnace having a plurality of circumferentially spaced charging openings and pyrometer tubes, means for rotating said furnace, and a stationary shield surrounding said furnace having a segmental portion containing openings and a pyrometer so arranged that when the furnace is rotated the charging openings and pyrometer tubes come into alinement respectively with the openings and the pyrometer, means operative to stop rotation of the furnace with a pyrometer tube and the adjacent charging openings in alinement respectively with the pyrometer and openings in said shield, and means operable after a predetermined time interval to start rotation of the furnace.

6. In a combination comprising a generallycircular, centrally fired heat treating furnace hav- A ing a plurality of circumferentially spaced charging openings and pyrometer tubes, means for rotating said furnace and a stationary shield surrounding said furnace having a segmental portion containing openings and a pyrometer so arranged that when the furnace is rotated the charging openings and pyrometer tubes come into alinement respectively with the openings and the pyrometer, means operative to stop rotation of the furnace with a pyrometer tube and the adjacent charging openings in `alinement respectively with the pyrometer and openings in said shield, means operable after a predetermined time interval to start rotation of the furnace, and temperature responsive means rendered operative during the stopping interval to prevent rotation of the furnace when the temperature is below a predetermined value.

7. In a combination comprising a generally circular, centrally iired heat treating furnace having a plurality of circumferentially spaced charging openings and pyrometer tubes, means for rotating said furnace and a stationary shield surrounding said furnace having a segmental portion containing openings and a pyrometer so arranged that when the furnace is rotated the charging openings and pyrometer tubes come into alinement respectively with the openings and the pyrometer, means operative to stop rotation of the furnace with a pyrometer tube and the adjacent charging openings in alinement respectively with the pyrometer and openings in said shield, means operable after a predetermined time interval to start rotation of the furnace, temperature responsive means rendered operative during the stopping interval to prevent rotation of the furnace when the temperature is below a predetermined value, and means rendering said temperature responsive means inoperative for a predetermined time interval after stopping rotation of the furnace.

8. In a combination comprising a generally circular, centrally fired heat treating furnace having a motor regulated burner, a plurality of circumferentially spaced charging openings and pyrometer tubes, means for rotating said furnace and a stationary shield surrounding said furnace having a segmental portion containing openings and a pyrometer so arranged that when the furnace is rotated the charging openings and pyrometer tubes come into alinment respectively with the openings and the pyrometer, means operative to stop rotationof the furnace with a pyrometer tube and the adjacent charging openings in alinement respectively with the pyrometer and openings in said shield, means operable after a predetermined time interval to start rotation of the furnace, and temperature responsive means rendered operative during the stopping interval to control operation of the burner regulating motor and prevent rotation of the furnace when the temperature is below a predetermined Value. y

9. In a combination comprising a generally circular, centrally red heat treating furnace having a motor regulated burner, a plurality of circumferentially spaced charging openings and pyrometer tubes, means for rotating said furnace and a stationary shield surrounding said furnace having a segmental portion containing openings and a pyrometer so arranged that when the furnace is rotated the chargingA openings and pyrometer tubes come into alinement respectively with the openings and the pyrometer, means operative to stoprotation of the furnace with a pyrometer tube and the adjacent charging openings in alinement respectively with the pyrometer and openings in said shield, means operable after a predetermined time interval to start rotation of the furnace, and temperature responsive means rendered operative during the stopping interval to control operation of the burner regulating motor and prevent rotation of the furnace When the temperature is below a predetermined value, and means rendering said temperature responsive means inoperative for a predetermined time interval after stopping rotation of the furnace.

l0. In combination with a motor driven rotary furnace having circumferentially spaced charging openings, means for obtaining temperature indications and switch actuating projections, a motor regulated burner and a magnetic braking mechanism for stopping the furnace, a control system comprising in circuit temperature responsive means controlling operation of said burner motor, an automatic switch controlling operation of said driving fnotor and braking mechanisrn, timing means controlling actuation of said automatic switch to energize the ydriving motor and release the brake, a retarded relay delaying operation of said timing and temperature responsive means and a switch actuated by said projections causing operation of said relay and automatic switch to deenergize the driving motor and apply the brake to stop rotation of the furnace with said temperature responsive means operatively associated With the means for obtaining temperature indications.

11. In combination with a motor driven rotary furnace having circumferentially spaced charging openings, means for obtaining temperature indications and switch actuating projections, a motor regulated burner and a magnetic braking mechanism for stopping the furnace, a control system comprising in circuit temperature responsive means controlling operation of said burner motor, an automatic switch controlling operation of said driving motor and braking mechanism, v

timing means controlling actuation of said automatic switch to energize the driving motor and release the brake, a retarded relay delaying operation of said timing and temperature responsive means, a switch actuated by said projections causprising in circuit a driving motor for rotating the furnace, a burner regulating motor, timing means operable when actuated 4to start said driving moltor after a predetermined time interval, temperature responsive means operable to control operation of said burner regulating motor and, when the temperature is below a predetermined value, to prevent actuation of said timing means to start rotation of the furnace, a retarded relay delaying operation of said timing and temperature responsive means and a switch responsive to furnace movement operable when actuated to cause operation of said relay and to stop said driving motor.

13. In a combination comprising a furnace control system having temperature responsive means including a temperature indicating device and a furnace having a plurality of spaced means for obtaining tempera-ture indications each of which is operatively associated with said device at spaced time intervals, means operable to render said system inoperative for a predetermined interval each time said association is established in order to insure a correct temperature indication and proper regulation of the furnace.

14. A heat treating furnace comprising a base having an upwardly extending firing tube, a side wall spaced from and surrounding said tube, a roof overlying said tube and base, means dividing the interior of the furnace into upper and lowercommunicating heating zones which surround said tube, and a plurality of spaced discharge fiues communicating at circumferentially spaced points with the lower portion of said lower heating zone.

15. In a combination comprising a furnace control system having temperature `responsive means including a temperature indicating device and a furnace having means for obtaining temperature indications which is operatively associated with said device at spaced intervals, means operable to render said system inoperative for a predetermined interval each time said association is established in order to insure a correct temperature indication and proper regulation of the furnace.

16. A heat treating furnace comprising a hearth, a means extending upward from the hearth and defining an upward flaring ame confining passage which is generally circular in cross section,7 a side w'all surrounding said means and forming with said means an annular heating zone surrounding said flame passage, a concave reflecting and deflecting surface overlying said passage and hearth, and discharge flue means communicating with said zone below the top of the flame passage-and adjacent the hearth and cooperating to cause the products of combustion issuing from said-passage to descend uniformly throughout the heating zone prior to their discharge therefrom. i

17. A heat treating furnace comprising a hearth having a centrally disposed means extending upward from the hearth and defining a flame confining passage which is generally circular in cross section and in which the cross sectional area progressivelyincreases towards the discharge end, a side wall surrounding said means and forming with said means an annular heating 18. A heat treating furnace comprising a hearth having a centrally disposed means extending upward from the hearth and dening an upward flaring flame confining passage which is generally circular in cross section, a side wall surrounding said means and forming with said means an annular heating zone surrounding said flame passage, one or more stock charging openings formed in said side wall at a point adjacent the hearth and below the top of the flame passage, a concave reflecting and deflecting surface overlying said passage and hearth, and discharge flue means communicating with the outer peripheral portion of said heating zone below said charging openings and cooperating to cause the products of combustion issuing from the flame passage to descend uniformly throughout the heating zone and past said charging openings and to cause cold air entering through the charging openings lto immediately pass downward adjacent the side wall and into the flue means.

19. A heat treating furnace comprising a hearth, a means extending upward from the hearth and defining a flame confining passage, a side wall forming with said means an annular heating zone surrounding the flame passage and having one or more stock charging openings located adjacent the hearth and below the top of the flame passage, a roof overlying said passage and hearth, and discharge flue means communicating with the outer peripheral portion of said heating zone below said charging openings and cooperating to cause the products of combustion issuing from said passage to descend uniformly throughout the heating zone and past the charging openings and to cause cold air entering through the charging openings to immediately pass downward adjacent the side wall and into the flue means.

20. In combination with a heat treating furnace comprising means including a hearth defining a heating zone having one'or more charging openings located adjacent the hearth and a burner means communicating with said zone at a point above said charging openings, means for preventing cold air entering the furnace through the charging openings from flowing over the hearth and cooling the stock disposed thereon comprising discharge flue means communicating with said heating zone at points near to and below the charging ,openings and operable to cause the Y products of combustion to descend past the charging openings and to cause cold air entering through said charging openings to immediately pass downward and into the discharge flue means.

HAROLD J. STEIN. 

